+---
+title: Boilers
+category: Mechanical
+toc_depth: 3
+description: >
+ When to use: Gas-fired and oil-fired hydronic (hot water) and low-pressure steam heating boilers for commercial, institutional, and industrial HVAC space-heating service. Covers condensing and non-condensing units, fire-tube and water-tube configurations, single and modular (multiple-boiler) plants, and packaged factory-assembled units from approximately 300 MBH input through the upper limit of low-pressure heating boiler service (15 psig steam; 160 psig and 250°F hot water). Addresses natural gas, propane, No. 2 fuel oil, and dual-fuel firing, with modulating and staged combustion controls and building automation system integration.
+
+ Not intended for: Domestic (potable) water heating, including instantaneous and storage water heaters and indirect-fired water heaters — see [[sync/water-heaters]]. High-pressure power boilers operating above 15 psig steam or above 160 psig / 250°F hot water (governed by ASME BPVC Section I, not Section IV, and outside the scope of this standard). Electric resistance and electrode boilers. Heat-recovery steam generators and waste-heat boilers. Process steam boilers serving manufacturing loads rather than building space heating. The hydronic distribution piping connected to the boiler is covered in [[sync/hydronic-piping]]; circulating pumps in [[sync/hvac-pumps]]; chemical treatment of the boiler water and condensate in [[sync/hvac-water-treatment]]; controls integration in [[sync/building-automation-system]]; and the fuel gas piping upstream of the boiler train in the project plumbing and fuel-gas standards.
+---
+
+# Scope
+
+This specification covers factory-assembled, packaged gas-fired and oil-fired heating boilers for hydronic (hot water) and low-pressure steam space-heating service in commercial, institutional, and industrial buildings. Equipment covered includes the pressure vessel or heat exchanger, the burner and integral fuel train, the combustion air and venting provisions, the boiler trim (relief valves, gauges, low-water cutoffs, and operating and limit controls), the burner-management and modulation controls, and the factory-mounted accessories furnished as part of the boiler assembly. Both single-boiler installations and modular plants of multiple smaller boilers staged together are addressed.
+
+A heating boiler covered by this standard operates within the low-pressure limits of ASME BPVC Section IV: 15 psig maximum for steam boilers, and 160 psig and 250°F maximum for hot water boilers. Equipment operating above these limits is a power boiler governed by ASME BPVC Section I and is outside this scope. The distinction matters because it determines the applicable construction code, the certification stamp, the relief valve type, and the controls and safety device requirements. The boundary of work under this standard is the boiler assembly itself, from the fuel train inlet connection and combustion air inlet through the flue outlet and the supply and return water (or steam and condensate) connections, including all factory-mounted trim and controls.
+
+Equipment shall comply with ASME BPVC Section IV for pressure-vessel construction, ASME CSD-1 for controls and safety devices on automatically fired boilers below 12,500,000 Btu/hr input, and NFPA 85 for boilers and combustion systems above the CSD-1 input threshold or where otherwise required by the Authority Having Jurisdiction. Gas-fired boilers shall additionally comply with CSA/ANSI Z21.13 / CSA 4.9 and the fuel-gas provisions of NFPA 54 (ANSI Z223.1). Oil-fired boilers shall comply with NFPA 31. Performance ratings shall conform to ANSI/AHRI 1500 with efficiency determined per ANSI/ASHRAE/AHRI 155. Minimum thermal efficiency shall comply with ANSI/ASHRAE/IES 90.1. Electrical components shall be listed to UL 795 or the applicable product listing. The Contractor shall coordinate boiler installation with the hydronic piping ([[sync/hydronic-piping]]), circulating pumps ([[sync/hvac-pumps]]), water treatment ([[sync/hvac-water-treatment]]), fuel-gas piping, venting, combustion air, electrical power, and the building automation system ([[sync/building-automation-system]]).
+
+# Referenced Standards
+
+Equipment, materials, and installation shall comply with the latest adopted edition of each of the following unless a specific edition is cited. Where conflicts exist between referenced standards, the more stringent requirement shall govern unless the Engineer of Record directs otherwise in writing.
+
+| Standard | Title |
+|----------|-------|
+| ASME BPVC Section IV | Rules for Construction of Heating Boilers |
+| ASME BPVC Section I | Rules for Construction of Power Boilers (boundary reference for units above low-pressure limits) |
+| ASME BPVC Section VI | Recommended Rules for the Care and Operation of Heating Boilers |
+| ASME CSD-1 | Controls and Safety Devices for Automatically Fired Boilers |
+| NFPA 85 | Boiler and Combustion Systems Hazards Code |
+| NFPA 54 / ANSI Z223.1 | National Fuel Gas Code |
+| NFPA 31 | Standard for the Installation of Oil-Burning Equipment |
+| CSA/ANSI Z21.13 / CSA 4.9 | Gas-Fired Low-Pressure Steam and Hot Water Boilers |
+| ANSI/AHRI 1500 (I-P) | Performance Rating of Commercial Space Heating Boilers |
+| ANSI/ASHRAE/AHRI 155 | Method of Testing for Rating Commercial Space Heating Boiler Systems |
+| ANSI/ASHRAE/IES 90.1 | Energy Standard for Buildings Except Low-Rise Residential Buildings |
+| UL 795 | Commercial-Industrial Gas Heating Equipment |
+| UL 1738 | Venting Systems for Gas-Burning Appliances, Categories II, III, and IV |
+| NFPA 70 | National Electrical Code (NEC) |
+| IMC | International Mechanical Code, adopted edition |
+| IBC / ASCE 7 | International Building Code / Minimum Design Loads and Associated Criteria for Buildings and Other Structures (seismic restraint) |
+| ASHRAE Handbook | HVAC Systems and Equipment (boiler application chapters) |
+
+# Submittals
+
+## Action Submittals
+
+The Contractor shall submit the following for the Engineer's review and approval prior to procurement. Fabrication and shipment shall not proceed until action submittals have been reviewed and returned.
+
+- Manufacturer's product data for each boiler, including model designation, configuration, input and output ratings, dimensions, operating and shipping weights, and required clearances
+- Rated performance data per ANSI/AHRI 1500, including input (MBH), gross output (MBH), thermal efficiency or combustion efficiency, and turndown ratio, with the rating basis and test standard (ANSI/ASHRAE/AHRI 155) identified
+- Pressure-vessel data: maximum allowable working pressure (MAWP), design temperature, ASME Section IV construction documentation, heat-exchanger material, and water content (gallons)
+- Burner data: burner type, fuel(s), firing range, modulation method, turndown ratio, NOx emission rating, and combustion air requirements
+- Fuel train (gas train or oil train) piping schematic showing all valves, regulators, safety shutoff valves, pressure switches, and the gas pressure or oil pressure required at the train inlet
+- Controls and safety device schedule demonstrating compliance with ASME CSD-1 (or NFPA 85 where applicable), including the burner-management system, flame safeguard, operating and high-limit controls, low-water cutoff(s), and relief valve sizing
+- Relief valve (or safety valve) selection showing set pressure, relieving capacity (BTU/hr or lb/hr), and ASME Section IV certification (HV mark)
+- Venting requirements: vent category (I through IV), required vent material, vent and combustion-air pipe size, and maximum and minimum equivalent vent length
+- Condensate drainage and, for condensing boilers, condensate neutralizer data including media type and replacement interval
+- Electrical data: voltage, phase, full-load amperes, minimum circuit ampacity, and maximum overcurrent protection
+- Wiring diagrams (ladder and point-to-point) showing all factory and field connections and BAS interface points
+- Seismic restraint calculations and details where required by the applicable building code
+
+```datasheet
+label: Action Submittals Required
+type: checkbox
+options:
+ - "Product data with input/output ratings and clearances"
+ - "AHRI 1500 rated performance (efficiency, turndown)"
+ - "Pressure-vessel data and ASME Section IV documentation"
+ - "Burner data with NOx rating and combustion air"
+ - "Fuel train piping schematic"
+ - "Controls and safety device schedule (CSD-1 / NFPA 85)"
+ - "Relief valve selection and ASME certification"
+ - "Venting category, material, and length"
+ - "Condensate neutralizer data (condensing boilers)"
+ - "Electrical data and wiring diagrams"
+ - "Seismic restraint calculations"
+default: "Product data with input/output ratings and clearances"
+```
+
+## Closeout Submittals
+
+At substantial completion, the Contractor shall provide the following before boilers are accepted.
+
+- Operation and maintenance manuals for each boiler, organized with a table of contents, including manufacturer's installation, startup, operation, and maintenance instructions
+- Manufacturer's Data Report (ASME Form H-2 or equivalent) for each boiler and the National Board registration number where the boiler is National Board registered
+- Factory hydrostatic test certificate for each pressure vessel
+- Manufacturer's startup and combustion-test report documenting measured combustion efficiency, flue-gas O2 or CO2, CO, stack temperature, and combustion settings at high fire and low fire
+- Burner-management and flame-safeguard configuration record
+- Relief valve certification and as-installed set pressure for each valve
+- As-built control sequence and BAS point list as commissioned
+- Warranty documentation, including the separate extended heat-exchanger warranty where provided
+- Spare parts inventory list with manufacturer part numbers
+
+# Quality Assurance
+
+## Manufacturer Qualifications
+
+Boilers shall be the products of a manufacturer with a minimum of ten years of continuous experience designing and producing commercial heating boilers of the type specified. The manufacturer shall maintain an ISO 9001 certified quality management system. Replacement parts and factory service support for the boiler model line shall be available for a minimum of fifteen years from the date of manufacture.
+
+## ASME Section IV Construction and Stamping
+
+The boiler pressure vessel shall be designed, fabricated, inspected, and stamped in accordance with ASME BPVC Section IV. Each boiler shall bear the ASME Certification Mark with the "H" designator (the heating-boiler stamp) and shall be furnished with a Manufacturer's Data Report. The H stamp certifies that the vessel is constructed for low-pressure heating service and may not be operated above 15 psig steam or 160 psig and 250°F hot water. Specifying ASME Section IV construction is the single most important quality requirement for a heating boiler; an unstamped or non-code vessel cannot be legally installed in most jurisdictions and cannot be insured for boiler-and-machinery coverage.
+
+```datasheet
+label: ASME Boiler Code Stamp
+type: radio
+options:
+ - "ASME Section IV 'H' stamp — low-pressure heating boiler (standard)"
+ - "ASME Section I 'S' stamp — power boiler (only if operating above Section IV limits; outside this standard's scope)"
+default: "ASME Section IV 'H' stamp — low-pressure heating boiler (standard)"
+```
+
+## National Board Registration
+
+Where required by the Authority Having Jurisdiction or by the Owner's boiler insurer, each boiler shall be registered with the National Board of Boiler and Pressure Vessel Inspectors, and the National Board registration number shall be recorded on the nameplate and in the closeout documentation. National Board registration provides an independent record of the vessel's construction and certification that survives changes of building ownership and supports future jurisdictional inspections.
+
+```datasheet
+label: National Board Registration
+type: radio
+options:
+ - "Required — register with the National Board"
+ - "Not required — verify with AHJ and Owner's insurer"
+default: "Required — register with the National Board"
+```
+
+## Controls and Safety Device Compliance
+
+The controls and safety devices on each automatically fired boiler shall comply with ASME CSD-1 where the boiler input is below 12,500,000 Btu/hr. For boilers at or above 12,500,000 Btu/hr input, or where the Authority Having Jurisdiction requires it, the controls and combustion-safety provisions of NFPA 85 shall govern. CSD-1 and NFPA 85 establish the required burner-management sequence, flame supervision, fuel safety shutoff, and limit-control redundancy that prevent the two principal boiler hazards: a fuel-air explosion in the combustion chamber, and a dry-fire (low-water) failure of the pressure vessel.
+
+```datasheet
+label: Combustion Safety Code
+type: radio
+options:
+ - "ASME CSD-1 — automatically fired boiler below 12.5 MMBtu/hr input"
+ - "NFPA 85 — boiler at or above 12.5 MMBtu/hr input or as required by AHJ"
+default: "ASME CSD-1 — automatically fired boiler below 12.5 MMBtu/hr input"
+```
+
+## Listing and Certification
+
+Gas-fired boilers shall be tested and certified to CSA/ANSI Z21.13 / CSA 4.9 by a Nationally Recognized Testing Laboratory and shall bear the certification mark. Electrical and combustion components shall be listed to UL 795 or the applicable product standard. The complete boiler assembly, including all electrical components, shall be listed by an NRTL.
+
+## Pre-Installation Conference
+
+A pre-installation conference shall be held before boiler installation begins, attended by the mechanical contractor, the controls contractor, the commissioning agent, the manufacturer's startup representative, and the Owner's representative. The agenda shall include rigging and setting, fuel-gas and combustion-air provisions, venting routing and material, water-treatment and fill procedures, the controls interface, and the startup and commissioning schedule.
+
+# Environmental and Service Conditions
+
+## Installation Location
+
+Boilers shall be selected and rated for the conditions at the installation site. Indoor mechanical-room installation is the standard commercial application. Outdoor and rooftop installation requires a weatherproof jacket, a listed outdoor-rated boiler, and freeze protection of the water side.
+
+```datasheet
+label: Boiler Installation Location
+type: select
+options:
+ - "Indoor — dedicated boiler/mechanical room"
+ - "Indoor — penthouse or rooftop mechanical room"
+ - "Outdoor — rooftop, weatherproof-listed unit"
+ - "Outdoor — grade-level, weatherproof-listed unit"
+default: "Indoor — dedicated boiler/mechanical room"
+```
+
+## Altitude Derating
+
+Where the project site is at an elevation above 2,000 ft (610 m), boiler input and combustion air shall be corrected for the reduced air density at altitude, and the burner shall be configured (orifice, air-fuel ratio, or factory high-altitude calibration) for the project elevation. Uncorrected combustion at altitude runs rich, reducing efficiency, increasing CO, and increasing sooting on oil-fired units. The required derating and burner configuration shall be documented in the submittal.
+
+```datasheet
+label: Project Site Elevation
+type: range
+unit: ft above sea level
+options:
+ min: 0
+ max: 10000
+ setpoints: [0, 1000, 2000, 3000, 4000, 5000, 6000, 8000, 10000]
+default: 0
+```
+
+# Boiler Type and Configuration
+
+## Heating Medium
+
+The heating medium determines the pressure vessel design, the trim, and the connected distribution system. Hot water boilers serve closed-loop hydronic distribution and are the dominant choice for commercial space heating because they operate at lower pressure and temperature, integrate readily with variable-flow distribution, and tolerate part-load operation efficiently. Low-pressure steam boilers serve steam distribution systems (often in older institutional campuses, or where steam is required for humidification or kitchen loads) and require condensate return and feedwater management not present in hot water systems.
+
+```datasheet
+label: Heating Medium
+type: radio
+options:
+ - "Hot water (hydronic) — closed loop"
+ - "Low-pressure steam (15 psig maximum)"
+default: "Hot water (hydronic) — closed loop"
+```
+
+## Condensing or Non-Condensing
+
+A condensing boiler extracts additional sensible and latent heat from the flue gas by cooling it below the water dewpoint (about 130°F flue temperature for natural gas), condensing the water vapor produced by combustion and recovering its heat of vaporization. This raises thermal efficiency to 88–95% but requires return water cool enough to sustain condensation (typically below 130–140°F), a corrosion-resistant heat exchanger, an acidic-condensate drain, and a Category IV vent. A non-condensing boiler operates with flue temperatures above the dewpoint, achieves about 80–85% efficiency, and must keep return water warm enough (typically above 140°F) to avoid sustained condensation that would corrode a heat exchanger not designed for it. Condensing boilers are the default selection for new construction because ASHRAE 90.1 efficiency minimums and low-temperature hydronic design favor them; non-condensing boilers remain appropriate for high-temperature systems and for retrofits into existing high-temperature distribution.
+
+```datasheet
+label: Condensing or Non-Condensing
+type: radio
+options:
+ - "Condensing — recovers latent heat, requires low return-water temperature"
+ - "Non-condensing — flue above dewpoint, requires return-water temperature protection"
+default: "Condensing — recovers latent heat, requires low return-water temperature"
+```
+
+## Heat Exchanger Configuration
+
+Fire-tube boilers pass hot combustion gas through tubes surrounded by water; they hold a large water volume, respond slowly, tolerate fluctuating loads well, and are common in larger single-boiler plants. Water-tube boilers pass water through tubes surrounded by hot gas; they hold a small water volume, respond quickly, and are common in modular condensing designs where rapid modulation and compact size matter. The selection interacts with the condensing decision: most high-efficiency condensing boilers are compact water-tube or finned-tube designs, while many large non-condensing boilers are fire-tube.
+
+```datasheet
+label: Heat Exchanger Configuration
+type: select
+options:
+ - "Fire-tube — large water volume, stable, larger single units"
+ - "Water-tube — low water volume, fast response, modular condensing"
+ - "Cast-iron sectional — assembled sections, field-serviceable"
+ - "Finned-tube (copper or stainless) — compact, low mass"
+default: "Water-tube — low water volume, fast response, modular condensing"
+```
+
+## Plant Arrangement
+
+The plant arrangement shall be [[drawing: as indicated on the mechanical equipment schedules and flow diagrams]]. A single boiler is simplest but provides no redundancy and is oversized for most of the heating season. A modular plant of multiple smaller boilers staged by load improves part-load efficiency (idle boilers do not lose heat up the stack), provides redundancy, and matches the wide turndown that condensing technology rewards. Most new commercial hydronic plants use two or more modular boilers.
+
+```datasheet
+label: Plant Arrangement
+type: select
+options:
+ - "Single boiler (no redundancy)"
+ - "Two boilers — lead/lag staging"
+ - "Modular plant — three or more boilers staged by load"
+ - "N+1 redundant — one boiler beyond design capacity"
+drawing_ref: true
+default: "Modular plant — three or more boilers staged by load"
+```
+
+# Capacity, Efficiency, and Turndown
+
+## Input and Output Capacity
+
+Each boiler's gross input and net output shall be [[drawing: as indicated on the mechanical equipment schedules]]. Capacity shall be selected on the rated output (the heat delivered to the water or steam), not the input, accounting for the building heating load, the system pickup factor, and the plant arrangement.
+
+```datasheet
+label: Boiler Input Capacity
+type: range
+unit: MBH
+drawing_ref: true
+options:
+ min: 300
+ max: 12000
+ setpoints: [300, 500, 750, 1000, 1500, 2000, 2500, 3000, 4000, 5000, 6000, 8000, 10000, 12000]
+default: 2000
+```
+
+## Thermal Efficiency
+
+Thermal efficiency shall meet or exceed the minimum required by ANSI/ASHRAE/IES 90.1 for the applicable boiler type and input capacity, with ratings established per ANSI/AHRI 1500 and tested per ANSI/ASHRAE/AHRI 155. Efficiency is the principal lifecycle-cost driver for a boiler — fuel cost over a 20-year service life vastly exceeds first cost — so the efficiency floor should be evaluated against the system return-water temperature that actually governs achievable performance. A condensing boiler operating on a high-temperature loop never condenses and delivers no better efficiency than a non-condensing unit; the efficiency selection and the hydronic design must be coordinated.
+
+```datasheet
+label: Minimum Thermal Efficiency
+type: range
+unit: "%"
+options:
+ min: 80
+ max: 96
+ setpoints: [80, 82, 84, 85, 88, 90, 92, 94, 95, 96]
+default: 90
+```
+
+## Turndown Ratio
+
+Turndown ratio is the ratio of maximum firing rate to minimum firing rate. Higher turndown lets a single boiler modulate down to match a small load without cycling on and off, which improves efficiency (each cycle incurs a pre-purge that sends room air up the stack) and reduces thermal stress on the heat exchanger. Modulating condensing boilers commonly achieve 5:1 to 10:1 turndown; staged or on-off non-condensing boilers achieve little or no turndown per boiler and rely on plant staging instead. High turndown is most valuable in single-boiler plants; in a modular plant the plant turndown comes from staging boilers, so per-boiler turndown is less critical.
+
+```datasheet
+label: Burner Turndown Ratio
+type: select
+options:
+ - "On-off (no modulation)"
+ - "2:1"
+ - "4:1"
+ - "5:1"
+ - "8:1"
+ - "10:1 or greater"
+default: "5:1"
+```
+
+## Maximum Operating Pressure and Temperature
+
+The boiler maximum allowable working pressure (MAWP) and design temperature shall equal or exceed the system operating conditions [[drawing: as indicated on the drawings]] and shall not exceed the ASME Section IV low-pressure limits. The relief valve set pressure and the system fill and expansion provisions shall be coordinated with the selected MAWP.
+
+```datasheet
+label: Maximum Allowable Working Pressure (Water)
+type: range
+unit: psig
+drawing_ref: true
+options:
+ min: 30
+ max: 160
+ setpoints: [30, 50, 60, 80, 100, 125, 160]
+default: 80
+```
+
+```datasheet
+label: Maximum Operating Water Temperature
+type: range
+unit: "°F"
+drawing_ref: true
+options:
+ min: 140
+ max: 250
+ setpoints: [140, 160, 180, 200, 220, 240, 250]
+default: 180
+```
+
+# Heat Exchanger and Pressure Vessel
+
+## Heat Exchanger Material
+
+The heat-exchanger material shall match the duty. Condensing boilers require a material that resists the carbonic acid formed when flue-gas water vapor condenses; stainless steel (typically Type 316L or 439) and certain aluminum-silicon alloys are the standard condensing materials. Non-condensing boilers may use cast iron, carbon steel, or copper because they are not exposed to sustained condensate. Specifying a cast-iron or carbon-steel exchanger for condensing duty is a common and costly error — the exchanger corrodes through within a few years. Likewise, aluminum exchangers require tighter water-chemistry control (pH and inhibitor compatibility) than stainless steel; see [[sync/hvac-water-treatment]].
+
+```datasheet
+label: Heat Exchanger Material
+type: select
+options:
+ - "Stainless steel (Type 316L or 439) — condensing service (standard)"
+ - "Aluminum-silicon alloy — condensing service (verify water chemistry compatibility)"
+ - "Cast iron — non-condensing service"
+ - "Carbon steel — non-condensing fire-tube service"
+ - "Copper finned-tube — non-condensing service"
+default: "Stainless steel (Type 316L or 439) — condensing service (standard)"
+```
+
+## Pressure Vessel Construction
+
+The pressure vessel shall be constructed and stamped per ASME BPVC Section IV as specified under Quality Assurance. Welded joints, tube-to-tubesheet connections, and section assembly shall follow the code-qualified procedures documented in the Manufacturer's Data Report. Each vessel shall be hydrostatically tested at the factory at the pressure required by Section IV before shipment.
+
+## Water Volume and Thermal Mass
+
+The boiler water volume affects control stability and minimum-flow requirements. Low-mass water-tube and finned-tube condensing boilers hold little water and are sensitive to low flow — inadequate flow causes rapid temperature rise across the exchanger, nuisance high-limit trips, and thermal stress. Low-mass boilers therefore require a minimum flow rate and frequently a primary (boiler) loop with its own circulator decoupled from the system loop. High-mass fire-tube and cast-iron boilers are more flow-tolerant. The minimum flow requirement and the loop arrangement shall be coordinated with [[sync/hydronic-piping]] and [[sync/hvac-pumps]].
+
+```datasheet
+label: Boiler Loop Arrangement
+type: select
+options:
+ - "Primary/secondary — dedicated boiler circulator and hydraulic separation"
+ - "Primary-only variable flow — boiler rated for variable flow with minimum-flow protection"
+ - "Direct — single loop (high-mass boilers only)"
+default: "Primary/secondary — dedicated boiler circulator and hydraulic separation"
+```
+
+# Burner and Fuel Train
+
+## Fuel
+
+The fuel shall be [[drawing: as indicated on the drawings]]. Natural gas is the default fuel for commercial heating where a gas utility is available. Propane serves sites without natural gas service and requires burner orifices and pressure settings specific to propane. Fuel oil (typically No. 2) serves sites without gas service or provides backup firing where utility gas is interruptible. Dual-fuel (gas/oil) boilers fire gas under normal conditions and switch to oil during gas curtailment, which some utility interruptible-rate tariffs require.
+
+```datasheet
+label: Fuel
+type: select
+options:
+ - "Natural gas"
+ - "Propane (LP gas)"
+ - "No. 2 fuel oil"
+ - "Dual-fuel — natural gas / No. 2 oil"
+drawing_ref: true
+default: "Natural gas"
+```
+
+## Burner Type and Modulation
+
+The burner shall be a power burner with forced or induced draft, matched to the boiler and certified as an assembly. Modulating burners continuously adjust firing rate to the load and are the standard for condensing boilers and for any single-boiler plant where turndown matters. Staged burners fire in discrete steps (low/high or low/medium/high). On-off burners are acceptable only in modular plants where plant staging provides the modulation.
+
+```datasheet
+label: Burner Modulation
+type: radio
+options:
+ - "Fully modulating — continuous firing-rate control"
+ - "Staged (two- or three-stage)"
+ - "On-off (modular plant staging only)"
+default: "Fully modulating — continuous firing-rate control"
+```
+
+## Fuel Train
+
+The gas train (or oil train) shall comply with ASME CSD-1 or NFPA 85 as applicable and with NFPA 54 for gas piping at the train. The train shall include the manual shutoff, pressure regulator, dual safety shutoff valves (with proof-of-closure where required by input rating), high and low gas-pressure switches, and the leak-test or valve-proving provisions required for the boiler input. The required inlet gas pressure shall be stated in the submittal and coordinated with the fuel-gas piping design; an undersized gas service or regulator that cannot deliver the required pressure at full fire is a common startup failure.
+
+```datasheet
+label: Fuel Train Compliance
+type: radio
+options:
+ - "ASME CSD-1 gas/oil train (below 12.5 MMBtu/hr)"
+ - "NFPA 85 gas/oil train (12.5 MMBtu/hr and above or as required by AHJ)"
+ - "FM Global approved train (where Owner's insurer requires)"
+default: "ASME CSD-1 gas/oil train (below 12.5 MMBtu/hr)"
+```
+
+## Low-NOx Compliance
+
+NOx emissions from the burner shall comply with the limit applicable to the project. NOx limits are set regionally by the local air-quality authority and are not uniform nationwide. In severe non-attainment areas — most notably the South Coast Air Quality Management District (SCAQMD) in Southern California under the Rule 1146 series — low-NOx (typically 30 ppm or below) or ultra-low-NOx (9 ppm, and 7 ppm for fire-tube boilers under recent amendments) burners are mandatory. Elsewhere, standard burners may be acceptable. The applicable limit shall be confirmed with the local air-quality authority for the project location; specifying a low-NOx limit where none is required adds cost, while overlooking a regional limit causes permitting failure.
+
+```datasheet
+label: NOx Emission Limit
+type: select
+options:
+ - "Standard burner — no regional low-NOx limit"
+ - "Low-NOx — 30 ppm or below"
+ - "Ultra-low-NOx — 20 ppm or below"
+ - "Ultra-low-NOx — 9 ppm (SCAQMD and similar severe non-attainment areas)"
+ - "Ultra-low-NOx — 7 ppm (fire-tube boilers, SCAQMD Rule 1146)"
+default: "Standard burner — no regional low-NOx limit"
+```
+
+# Combustion Air and Venting
+
+## Combustion Air Source
+
+The combustion air source shall be selected for the installation. Direct-vent (sealed-combustion) boilers draw combustion air through a dedicated pipe from outdoors directly to the burner, isolating combustion from the mechanical-room air; this is required for condensing boilers in tight mechanical rooms and is the standard for new construction. Room-air (indoor-air) combustion draws air from the mechanical room, which then requires permanent combustion-air openings sized per NFPA 54 or the IMC. Drawing combustion air from the room competes with building exhaust and can cause backdrafting and CO hazards if the room air is depressurized.
+
+```datasheet
+label: Combustion Air Source
+type: radio
+options:
+ - "Direct-vent (sealed combustion) — dedicated outdoor air intake pipe"
+ - "Room air — mechanical-room combustion-air openings per NFPA 54 / IMC"
+default: "Direct-vent (sealed combustion) — dedicated outdoor air intake pipe"
+```
+
+## Vent Category
+
+The vent category established by CSA/ANSI Z21.13 classifies the appliance by flue pressure (positive or negative) and flue temperature (above or below dewpoint), and it governs the required vent material. Category I is negative-pressure, non-condensing (natural-draft or draft-assisted), vented with conventional Type B or single-wall vent. Category III is positive-pressure, non-condensing, requiring a listed gas-tight stainless vent. Category IV is positive-pressure, condensing — the category of most modern condensing boilers — requiring a listed gas-tight, corrosion-resistant vent (AL29-4C stainless, polypropylene, or CPVC per the manufacturer's listing). The vent material must match the appliance category; using a Category I vent on a Category IV condensing boiler causes condensate leakage and flue-gas escape.
+
+```datasheet
+label: Vent Category
+type: select
+options:
+ - "Category I — negative pressure, non-condensing"
+ - "Category II — negative pressure, condensing (rare)"
+ - "Category III — positive pressure, non-condensing"
+ - "Category IV — positive pressure, condensing (most condensing boilers)"
+default: "Category IV — positive pressure, condensing (most condensing boilers)"
+```
+
+## Vent Material
+
+Vent material shall be listed to UL 1738 for Category II, III, and IV appliances, or shall be the conventional vent listed for Category I appliances. The selected material shall match the vent category, the flue-gas temperature, and the manufacturer's installation instructions, and shall be rated for the equivalent vent length of the actual routing [[drawing: as indicated on the drawings]].
+
+```datasheet
+label: Vent Material
+type: select
+options:
+ - "Type B double-wall vent — Category I"
+ - "Single-wall metal vent — Category I (where permitted)"
+ - "AL29-4C special stainless — Category III/IV"
+ - "Polypropylene (PP) — Category IV (per manufacturer listing)"
+ - "CPVC — Category IV (within temperature limit, per manufacturer listing)"
+default: "AL29-4C special stainless — Category III/IV"
+```
+
+# Controls and Safety Devices
+
+## Burner-Management and Flame Safeguard
+
+Each boiler shall be furnished with a burner-management (flame-safeguard) control that executes the purge, ignition trial, run, and post-purge sequence and proves flame throughout firing. Loss of flame shall lock out the burner and require manual reset. The flame-safeguard control and its sequence shall comply with ASME CSD-1 or NFPA 85 as applicable. The pre-purge that clears unburned fuel from the chamber before ignition is the primary defense against a combustion-chamber explosion and shall not be defeated.
+
+## Operating and Limit Controls
+
+Each boiler shall have an operating control that cycles or modulates the burner to maintain the setpoint, and a separate high-limit (operating-limit) control, independent of the operating control, that shuts down the burner if temperature or pressure exceeds the safe limit. A manual-reset high-limit shall be provided where required by CSD-1. Hot water boilers shall have a temperature high-limit; steam boilers shall have a pressure high-limit.
+
+```datasheet
+label: High-Limit Control
+type: radio
+options:
+ - "Auto-reset operating limit plus manual-reset safety high-limit (CSD-1 standard)"
+ - "Auto-reset operating limit only (where permitted by input and AHJ)"
+default: "Auto-reset operating limit plus manual-reset safety high-limit (CSD-1 standard)"
+```
+
+## Low-Water Cutoff
+
+Each boiler shall be equipped with a low-water cutoff that shuts off the burner before the water level falls low enough to expose heating surfaces and dry-fire the vessel. Dry-firing is the most destructive boiler failure mode — heating surfaces overheat, distort, and can rupture. CSD-1 requires a low-water cutoff on every automatically fired boiler, and a second (redundant) low-water cutoff is required above a threshold input or by many jurisdictions. Steam boilers and most hot water boilers shall have the cutoff(s); a manual-reset cutoff is preferred so that an operator investigates the cause before the boiler restarts.
+
+```datasheet
+label: Low-Water Cutoff
+type: radio
+options:
+ - "Single auto-reset low-water cutoff"
+ - "Primary plus secondary (redundant) low-water cutoff (standard for larger boilers)"
+ - "Primary plus secondary, manual-reset secondary"
+default: "Primary plus secondary (redundant) low-water cutoff (standard for larger boilers)"
+```
+
+## BAS Integration
+
+The boiler controls shall integrate with the building automation system per [[sync/building-automation-system]]. The boiler control shall accept a remote enable and a remote setpoint or firing-rate command, and shall report status, firing rate, supply and return temperature (or steam pressure), and alarms. In modular plants, the plant lead-lag controller (boiler-mounted master or BAS-resident) shall stage and rotate the boilers to balance runtime and optimize part-load efficiency. Communications protocol and interface points shall be coordinated with the BAS contractor prior to submittal.
+
+```datasheet
+label: BAS Communication Protocol
+type: select
+options:
+ - "BACnet MS/TP (RS-485)"
+ - "BACnet IP (Ethernet)"
+ - "Modbus RTU (RS-485)"
+ - "Modbus TCP/IP (Ethernet)"
+ - "Hardwired (enable, alarm, and 0-10V firing-rate only)"
+default: "BACnet IP (Ethernet)"
+```
+
+## Outdoor Air Reset and O2 Trim
+
+Hot water boiler plants should reset the supply-water temperature setpoint downward as the outdoor temperature rises (outdoor air reset), because a lower supply temperature increases the hours of condensing operation and reduces standing and distribution losses. Larger plants may include combustion (O2) trim, which measures flue-gas oxygen and continuously adjusts the air-fuel ratio to hold optimal excess air as ambient conditions, fuel quality, and burner wear vary. O2 trim is most cost-effective on large, continuously firing boilers; it adds little benefit to small modular boilers that cycle.
+
+```datasheet
+label: Combustion Optimization
+type: select
+options:
+ - "Outdoor air reset of supply-water setpoint (standard for hot water)"
+ - "Outdoor air reset plus O2 trim (large continuously firing boilers)"
+ - "Fixed setpoint, no reset"
+default: "Outdoor air reset of supply-water setpoint (standard for hot water)"
+```
+
+# Water Connections and Trim
+
+## Relief Valve
+
+Each boiler shall be furnished with an ASME-rated pressure relief valve (hot water) or safety valve (steam), certified to ASME BPVC Section IV and bearing the ASME certification mark with the HV designator. The valve relieving capacity shall equal or exceed the boiler gross output, and the set pressure shall not exceed the boiler MAWP. The relief valve is the last-line protection against overpressure; it shall be piped full-size to a safe discharge point without any intervening valve, and its discharge shall terminate where escaping hot water or steam cannot injure personnel.
+
+```datasheet
+label: Relief / Safety Valve
+type: radio
+options:
+ - "ASME Section IV pressure relief valve (hot water boiler)"
+ - "ASME Section IV safety valve (steam boiler)"
+default: "ASME Section IV pressure relief valve (hot water boiler)"
+```
+
+## Boiler Trim
+
+Each boiler shall be furnished with the trim required by ASME Section IV and CSD-1 for the heating medium: hot water boilers with a combination temperature-pressure gauge, an ASME relief valve, and a drain valve; steam boilers with a steam pressure gauge, a water-level gauge glass with try-cocks, an ASME safety valve, and a blowdown valve. All trim shall be factory-mounted and piped to the extent practical to minimize field connections.
+
+```datasheet
+label: Trim Package
+type: checkbox
+options:
+ - "Temperature-pressure gauge (hot water)"
+ - "Steam pressure gauge (steam)"
+ - "Water-level gauge glass with try-cocks (steam)"
+ - "ASME relief / safety valve"
+ - "Drain / blowdown valve"
+ - "Air vent connection (hot water)"
+ - "Thermometer wells for supply and return"
+default: "ASME relief / safety valve"
+```
+
+## Water Connections
+
+Supply and return (or steam and condensate) connections shall be flanged or grooved to match the connected hydronic piping, sized for the boiler design flow, and located to permit complete venting of air from the vessel. Connections to [[sync/hydronic-piping]] shall include isolation valves at each boiler so a single boiler can be isolated and serviced without draining the plant.
+
+# Factory and Field Testing / Commissioning
+
+## Factory Tests
+
+The manufacturer shall hydrostatically test each pressure vessel per ASME Section IV before shipment and shall furnish the test certificate. Where the burner and boiler are factory fire-tested as an assembly, the manufacturer shall furnish the factory combustion-test data.
+
+## Field Startup and Commissioning
+
+A factory-authorized startup technician shall perform the initial firing and combustion setup of each boiler. Startup shall verify the fuel-train leak test, the burner-management sequence (purge, ignition trial, flame proof, lockout on flame loss), the operating and high-limit controls, the low-water cutoff function (by lowering the water level or simulating the condition), and the relief-valve set pressure. The technician shall set and record combustion at high fire and low fire, documenting flue-gas O2 or CO2, CO, stack temperature, and the resulting combustion efficiency. NFPA 85 requires a written commissioning plan for the boilers within its scope; where NFPA 85 applies, the plan shall be submitted and followed.
+
+```datasheet
+label: Startup Combustion Test Documentation
+type: checkbox
+options:
+ - "Fuel-train leak test record"
+ - "Burner-management sequence verification"
+ - "Low-water cutoff function test"
+ - "High-limit and operating-control test"
+ - "Relief-valve set-pressure verification"
+ - "Combustion readings at high and low fire (O2/CO2, CO, stack temp, efficiency)"
+default: "Combustion readings at high and low fire (O2/CO2, CO, stack temp, efficiency)"
+```
+
+The commissioning agent shall witness the functional tests, verify the BAS points and the plant staging/lead-lag rotation, and confirm outdoor-air reset operation. The boiler water shall be filled, treated, and verified per [[sync/hvac-water-treatment]] before sustained firing; firing a hydronic boiler on untreated or improperly treated water voids most heat-exchanger warranties.
+
+# Installation
+
+## Setting and Clearances
+
+Boilers shall be set level on a housekeeping pad as detailed on [[drawing: the structural and mechanical drawings]], with the manufacturer's required service and code clearances maintained on all sides, including tube-pull clearance for fire-tube and water-tube units and section-removal clearance for cast-iron sectional boilers. Clearances to combustible construction shall comply with the listing and the IMC. Crowding a boiler into a tight room without tube-pull clearance makes future heat-exchanger service impossible without demolishing adjacent equipment.
+
+```datasheet
+label: Service Clearance Basis
+type: radio
+options:
+ - "Manufacturer's listed clearances plus tube-pull / section-removal access"
+ - "Code minimum clearances only (where space-constrained, with Engineer approval)"
+default: "Manufacturer's listed clearances plus tube-pull / section-removal access"
+```
+
+## Venting and Combustion Air
+
+The vent shall be installed per the manufacturer's instructions and the selected category and material, pitched to drain condensate back to the boiler (Category IV) or to a condensate drain, with all joints sealed gas-tight for positive-pressure categories. Vent and combustion-air terminations shall be located and separated per the manufacturer's listing and the IMC to prevent flue-gas recirculation into the air intake. Combustion-air provisions shall be completed and verified before startup.
+
+## Condensate Drainage and Neutralization
+
+Condensing boilers produce acidic condensate (pH approximately 3 to 5) that shall be drained to a code-compliant disposal point. Where the condensate is discharged to a sanitary drain that does not have sufficient dilution or where local code requires it, a condensate neutralizer (limestone or magnesium-oxide media) shall be installed to raise the pH before discharge. The neutralizer media is consumed over time and shall be listed in the O&M manual with a replacement interval. Discharging untreated boiler condensate corrodes metallic drain piping and can violate the local sewer-discharge code.
+
+```datasheet
+label: Condensate Neutralizer (Condensing Boilers)
+type: radio
+options:
+ - "Neutralizer required — discharge to sanitary with media (limestone/MgO)"
+ - "Neutralizer not required — verified acceptable per local code and drain material"
+ - "Not applicable — non-condensing boiler"
+default: "Neutralizer required — discharge to sanitary with media (limestone/MgO)"
+```
+
+## Seismic Restraint
+
+Where required by the IBC and ASCE 7 based on the seismic design category and the equipment importance factor, boilers shall be anchored and restrained. Restraints shall accommodate the design seismic forces while maintaining the fuel-train, vent, and piping connections intact. Boilers serving essential facilities (Ip = 1.5) require restraint designed for continued post-event function.
+
+```datasheet
+label: Seismic Restraint Required
+type: radio
+options:
+ - "Yes — per IBC and ASCE 7 (verify seismic design category)"
+ - "Yes — essential facility (Ip = 1.5)"
+ - "No"
+default: "No"
+```
+
+# Delivery, Storage, and Handling
+
+Boilers shall be delivered in the manufacturer's packaging with rigging points, lifting instructions, and the operating and shipping weights clearly marked. Units shall be protected from weather and physical damage until installed. Boilers stored before installation shall be kept dry and covered; the heat exchanger, burner, and controls shall not be exposed to moisture or construction dust. Where a boiler is set in place before the building is enclosed, it shall be covered and its openings sealed to keep debris out of the combustion chamber and the water side. Rigging shall use only the manufacturer's designated lifting points; lifting on trim, the jacket, or piping connections damages the unit.
+
+# Warranty
+
+The manufacturer shall warrant the complete boiler against defects in materials and workmanship for a minimum of one year from substantial completion. The heat exchanger (pressure vessel) shall carry a separate extended warranty: a minimum of ten years for condensing stainless-steel and aluminum exchangers and for cast-iron sectional exchangers, with longer terms available. The heat-exchanger warranty is typically conditioned on documented water treatment and, for condensing units, on maintaining return-water temperature and condensate drainage within the manufacturer's limits; the Contractor shall provide the commissioning and water-treatment records required to validate the warranty.
+
+```datasheet
+label: Heat Exchanger Warranty Term
+type: select
+options:
+ - "10 years (standard for condensing and cast-iron exchangers)"
+ - "12 years"
+ - "15 years"
+ - "20 years / limited lifetime (where offered)"
+default: "10 years (standard for condensing and cast-iron exchangers)"
+```
+
+# Spare Parts
+
+The Contractor shall furnish the manufacturer's recommended spare parts for the first year of operation, including ignition electrodes or igniters, flame-sensing components, gaskets for any access or burner doors opened during routine service, and one set of fuel-train filter elements where applicable. For modular plants, common wear parts shall be stocked once rather than per boiler. The spare-parts list with manufacturer part numbers shall be included in the closeout documentation.
+
+```datasheet
+label: Spare Parts Package
+type: checkbox
+options:
+ - "Ignition electrodes / hot-surface igniter"
+ - "Flame sensor / flame rod"
+ - "Burner and access-door gaskets"
+ - "Fuel-train filter elements"
+ - "Condensate neutralizer media (condensing boilers)"
+ - "Recommended controls spares (relays, sensors)"
+default: "Ignition electrodes / hot-surface igniter"
+```